1. Field of the Invention
The present invention relates to a clutch mechanism, especially for a motor vehicle.
In general terms the invention relates to a friction clutch, especially for a motor vehicle, and more particularly relates to a clutch equipped with a take-up or compensating device for wear which is due in particular to wear in the friction liner or liners, this device working to the extent that wear takes place in the liner or liners.
The invention relates to the friction clutch mechanism which is included in such clutches.
2. Description of the Related Art
A conventional clutch mechanism includes, in particular, a cover plate, a pressure plate coupled in rotation to the cover plate while being displaceable axially with respect to the latter, engagement means carried by the pressure plate, and axially acting clutch engagement means which act between the cover plate and the engagement means.
The clutch also includes a reaction plate which is part of an engine flywheel, which may be in two parts so as to form a damped flywheel or a flexible flywheel, mounted in rotation on a first shaft, which is typically a driving shaft such as the crankshaft of the internal combustion engine associated with the clutch, and supporting through its outer periphery the cover plate to which the pressure plate is attached with axial mobility.
The pressure plate is fixed in rotation to the cover plate and the reaction plate, while being displaceable axially under the action of axially acting clutch engagement means controlled by declutching means.
The declutching means may consist in a known way of helical springs, or two Belleville rings mounted in series, which are acted on by declutching levers that constitute the declutching means.
Generally, the clutch engaging and declutching means are both part of a common component, for example a metallic diaphragm which bears on the base of the cover plate. The diaphragm may be mounted in series or in parallel with a Belleville ring so as to provide assistance to the declutching force.
A friction disc, which typically carries friction liners at its outer periphery and which is fixed in rotation to a shaft, typically a driven shaft such as the input shaft of the gearbox of the propulsion engine unit, is interposed between the pressure plate and the reaction plate in such a way as to be gripped between them when the clutch is in its engaged position, for transmitting the torque from the driving shaft to the driven shaft. Conventionally, the friction liners are mounted on an axially elastic support member, which is coupled rigidly or elastically to a hub that is mounted in rotation on the driven shaft. Thanks to this arrangement, the friction disc assists the diaphragm during the declutching operation of the clutch.
In another version, the support member is encapsulated in a friction liner. In all cases the friction disc includes at least one friction liner, and has two friction faces for cooperation with the pressure plate and the reaction plate respectively.
The clutch engaging means, the cover plate and the pressure plate are part of a unitary assembly which is referred to as a friction clutch mechanism.
The clutch engaging means control the axial displacement of the pressure plate when they are actuated by a clutch release bearing through declutching means.
In the course of the working life of such a clutch, the friction liner or liners and the counter-acting materials, pressure and reaction plates, become worn, which causes a variation to occur in the axial position of the pressure plate and that of the axially acting clutch engaging means, as well as the clutch release bearing, and the result of this is a variation in the gripping force exerted between the friction disc on the one hand and the pressure and reaction plates on the other, because of the modifications of the working conditions of the clutch engaging means. The force which is necessary for disengagement is thereby affected. By giving such a clutch a wear compensating device these disadvantages are avoided, and the clutch engaging means, together with the clutch release bearing, which is typically in constant engagement on the clutch engaging means, then occupies the same position when the clutch is in its engaged condition, so that the axial size of the clutch is reduced.
In French patent application FR-A-2 753 503, applied for on Sep. 17, 1996, there is proposed a wear compensating device which comprises, firstly, ramp means fixed in rotation to an external set of teeth and placed between the pressure plate and the engagement means so as to constitute a pressure plate of variable thickness between its friction face, for engaging the appropriate friction liner of the friction disc, and the engagement means, and including, secondly, a cassette which is mounted in a housing of the cover plate and which includes a worm in cooperation with the set of teeth of the ramp means, and of the type in which the engagement means, the external set of teeth and the ramps are all part of a single component, in the form of an annular adjusting ring carried by the pressure plate.
The worm of the cassette is in cooperation with the teeth of the set of teeth that are part of the adjusting ramp ring which is placed between the clutch engaging means and the pressure plate.
The worm is in cooperation both with the set of teeth and with means for driving in rotation which comprise a helical spring, and which are rendered operational by wear in the friction liners when the clutch is engaged. The worm is mounted tangentially with respect to the set of teeth associated with it. In another version, the set of teeth is part of an intermediate member, as described in the document FR 98 11991 applied for on Sep. 23, 1998, coupled in rotation to the ramp ring by a coupling which permits this ring to move axially.
In the document FR-A-2 402 114, a solution was proposed for improving the operation of such a wear compensating device so that, on the occurrence of axial vibration produced by the crankshaft of the engine, or in the event of an overtravel of the clutch engaging means during the declutching operation, the ramps do not rotate and no take-up of wear takes place. More precisely, in the said document FR-A-2 402 114, a plurality of elastic attachments in the form of loops act between the adjusting ramp ring and the pressure plate.
Each attachment is fixed to an internal ear of the ring, and has a free end in contact with an ear of the pressure plate.
In that document, the adjusting ring is fixed in rotation by means of axial projections of the pressure plate which penetrate into complementary apertures formed in the adjusting ramp ring. The adjusting ring therefore does not have as simple a form as is desirable.
An object of the present invention is to mitigate this drawback, while continuing to benefit from improved operation of the wear compensating device.